1. Field of the Invention
The present invention relates to a rangefinder apparatus for measuring the distance to an object to be measured; and, in particular, to an active type rangefinder apparatus suitably used in a camera or the like.
2. Related Background Art
In active type rangefinder apparatus used in cameras and the like, an infrared light-emitting diode (IRED) projects a luminous flux toward an object to be measured, the reflected light of thus projected luminous flux is received by a position sensitive detector (PSD), a signal outputted from the PSD is arithmetically processed by a signal processing circuit and an arithmetic circuit and then is outputted as distance information, and the distance to the object is detected by a CPU. In general, since errors may occur when the distance is measured upon a single light-projecting operation, light is projected a plurality of times so as to obtain a plurality of distance information items, which are then accumulated at predetermined intervals by an integrating circuit so as to be integrated and averaged.
In such a rangefinder apparatus, it is preferred that the period of each accumulating operation and the number of accumulating operations in the integrating circuit be set to values corresponding to the external light luminance. Namely, from the viewpoint of improving the accuracy in distance measurement, it is preferable that the period of each accumulating period be elongated when the external light luminance is lower than when it is higher.